A couple of weeks ago my old CRT monitor gave up the ghost . It's now been replaced with an LCD panel. In the manual for the new monitor it says that it's very important that the monitor be turned on before the computer is. I've read such statements in other monitor manuals before too.

Does any one know if this warning is true, and if so why? What bad thing could happen if the monitor is usually turned on after the computer (in particular the graphics card signal is present)? I've googled this and found nothing.

FWIW I usually didn't obey this rule with my old monitors, and they seemed to live a reasonable time, but with the new one I'm trying to obey it for now.

I have an older LCD from around 2004/2005 that will give the "no signal" error message if it is not turned on before the PC. I don't think it damages anything as it now on my wife's PC and still working fine.

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Thanks, that's interesting. It sounds like for that one the "no signal" screen could be a safety feature to prevent some problem when it's used wrong, perhaps. My new monitor though will sync to the signal if it's turned on after.

There's another side to this apart from the power-on order at the start or end of a computer on/off cycle.

If you're using the DPMS features of X, such as setting the StandbyTime in xorg.conf, then when the inactivity timeout arrives, X shuts off the video signal. The monitor then shuts off the backlight and the power light goes orange, but it's still on. Once there's activity again (keyboard or mouse), the signal is restored and the monitor will come back on. This should be OK because it was never off before the "computer came back on".

Where it gets tricky, it seems, is that the monitor can be configured to turn off completely after 3 minutes of no signal. If you enable that feature (to save more power), and if you want to obey the power-on order rule, then there's a potential problem. You need to turn the monitor back on by hand before doing any activity that would restart the signal. But, you can't be sure of doing this because there can be accidental mouse activity that restarts the signal while the monitor is off, and of course you can't see that it happened! So you could be turning the monitor on after the signal is back. ISTM to avoid this you have to leave the 3-minute power-off feature disabled.

I haven't had issues with the ordering of monitors/computers in many years.

However, back in the day, it used to be very important that the monitor was turned on first. Some PCs, if it didn't detect a video signal at boot, would disable the video port completely. Again, hasn't been an issue in many years, but if you are using ancient hardware (pre-P4 I think), then it's something to watch out for.

Well from personal experience, a machine that's older than that never had any problems with monitors being off on startup.

On the other hand a P4 machine had a small issue with a CRT monitor. If I started it without the monitor being on and then switched it on it would display a low intensity image. If I rebooted the machine with the monitor still being on the display would have a normal intensity again.

Well from personal experience, a machine that's older than that never had any problems with monitors being off on startup.

Thanks Beastie. Yes, I also didn't have a problem with the previous machine, an AMD K6-2 500 (similar to Pentium). I guess it could be very specific to the design of some machines, to decide to turn off the graphics signal if no monitor is detected. Even that is not so bad, no damage would occur, and you could just reboot.

Older monitors needed sync signals from the computer when you turned them on. Otherwise, the CRT "beam" would sit in the middle of the screen and burn it out or heat up the internal circuitry. CRTs soon added protection for that, of course.

Thanks drhowarddrfine. That would explain such warnings on older monitors, though I never had that problem with the IBM (the manual warning could take on a life of its own for some time I suppose). I don't think the TTX had that problem either, though it's been a long time ... it's still packed away in storage, might even work.

Being, uh, frugal, I have six CRT monitors, five in storage. Three are from computers I bought from 1998 to 2001. Two are only lightly used. I will wait till they all burn out before I buy a flat screen monitor.